Just done a quick test to see just how much is clipped, and it refreshed on 2 seconds (2.41 GCD), this means, there is still 1 second where you can hit that last tick and get full damage and as you know, this is stronger. Going with the numbers I calculated;

Full Goring Blade Potency = 2420 over 9 GCDs = 268.89
Goring missing one tick, no fracture = 2370 over 9 GCDs = 263.33
Goring missing one tick with Fracture = 2640 over 10 GCDs = 264

So, going back to the first point, technically, there is a 1/3 chance you get the full Goring potency, and 2/3 chance you get the reduced potency, so average them out (268.89 + [2*263.33])/3 = 265.19 Potency per GCD on average, which is still higher than the rotation with Fracture, by 1.85 Potency per GCD. Adding in the slashing debuff and it increases to 2.43 Potency per GCD.

In conclusion then, it is still better, on average, to exclude Fracture from the rotation, unless you know you are missing that tick from Goring Blade (which realistically, noone can do). As for when it will be a potency increase, you effectively need to guarantee you miss that last tick, so you are looking for 21 seconds of Goring Blade, which, divided by 9, gets you to 2.33 GCD needed before fracture is, on average, better than Goring Blade.